Machine Design - GATE practice papers - Mechanical

1)   What is the effect of plating on the fatigue strength of a machine element?(Marks: 02)
- Published on 19 Oct 15

a. plating increases fatigue strength of a machine element
b. plating decreases fatigue strength of a machine element
c. plating does not affect fatigue strength of a machine element
d. unpredictable
Answer  Explanation 

ANSWER: plating decreases fatigue strength of a machine element

Explanation:
The internal residual stresses importantly affect the fatigue strength of a machine element. These internal residual stresses are affected by plating. Thus plating decreases fatigue strength of a machine element.


2)   Maximum principles stress theory by Rankine is applicable for those materials which are __________(Marks: 02)
- Published on 19 Oct 15

a. strong in shear but weak in tension or compression
b. weak in shear but strong in tension or compression
c. strong in shear as well as in tension or compression
d. weak in shear as well as in tension or compression
Answer  Explanation 

ANSWER: strong in shear but weak in tension or compression

Explanation:
The Rankine theory predicts the failure behavior of brittle material like cast iron. Brittle materials are strong in shear but weak in tension or compression.


3)   Why is the maximum stress applied to any machine element should always be less than its ultimate stress or critical stress? (Marks: 02)
- Published on 19 Oct 15

a. for safety against machine failure
b. to make complete use of mechanical properties of the machine element
c. both a. and b
d. none of the above
Answer  Explanation 

ANSWER: both a. and b

Explanation:
To design any machine element, safety is always considered as an important factor. Also to make use of mechanical properties of the machine element before its failure, it is designed in such a manner that the maximum applied stress should be less than its ultimate stress or critical stress. This applied stress is called as allowable stress or working stress.


4)   The load which can vary in magnitude as well as in direction is called as ________(Marks: 01)
- Published on 19 Oct 15

a. static load
b. dynamic load
c. both a. and b.
d. none of the above
Answer  Explanation 

ANSWER: dynamic load

Explanation:
Dynamic loads vary in magnitude as well as direction whereas static loads do not vary in direction.


5)   The ratio of critical stress to allowable stress is called as ___________(Marks: 01)
- Published on 19 Oct 15

a. factor of stress
b. factor of strength
c. factor of safety
d. none of the above
Answer  Explanation 

ANSWER: factor of safety

Explanation:
Factor of safety is the ratio of critical stress (or ultimate stress) to allowable stress (or working stress). Higher the value of factor of safety, lower will be the risk of failure of machine element.


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